A plurality of heat generating electronic components such as an arithmetic processing unit and a semiconductor element are incorporated in a casing of an electronic control unit mounted in a vehicle such as an engine control unit and a control unit for automatic transmission, and an internal temperature tends to increase. Therefore, a heat dissipation structure has been developed in which heat generated by electronic components is transferred to a casing of a device and released from a surface of the casing to the outside of the casing (for example, PTL 1).
Further, in recent years, the thermal environment of an electronic control unit mounted in a vehicle is increasingly severe. Background is that the electronic control unit is exposed to a higher temperature than ever since the installation location is changed from the inside of a vehicle to an engine room and on-engine, and also since heat generation per volume increases due to miniaturization of the electronic control unit. Further, with such change in the mounting environment, level of vibration/impact resistance required to the electronic control device increases.